1. Field of the Invention
The present invention relates to controlling the temperature of bearings of a cylinder of a printing press and a method for controlling a temperature of the bearings of the cylinder.
2. Description of the Related Art
In an intaglio rotary printing press, ink is supplied to an intaglio plate cylinder by an inking device. Redundant ink except that on the intaglio surface is wiped off by a wiping roller. The remaining ink on the intaglio surface is transferred onto paper which is passed between the intaglio plate cylinder and an impression cylinder in order to print onto the paper.
Ink commonly used for such an intaglio printing press has relatively high viscosity. If the temperature of the intaglio surface of an intaglio plate cylinder is too low, ink is not transferred satisfactorily to the intaglio surface, and ink is not dispersed into narrow grooves of the intaglio surface. For this reason, the intaglio plate cylinder has to be heated to between 60.degree. C. and 90.degree. C.
To heat the intaglio plate cylinder, commonly a path for heated water is provided near the inner surface of the intaglio plate cylinder. The heated water is circulated in a zigzag path by means of a rotary joint provided at the plate cylinder axle which is connected to a water heating unit.
Heated water passed through the plate cylinder axle results in the bearing for the axle becoming thermally expanded. On the other hand, in such a printing press, the bearing gap must be as small as is possible (minus tolerance) in order to maintain printing quality and also to prevent the bearings from fretting.
While a bearing housing mounted on the frame of the printing press machine and also the frame remain cool, the plate cylinder axle is thermally expanded. This results in an overload applied to the bearings, and the bearings become damaged.
When the temperature of the printing cylinder and its axle are raised, the bearing gap is reduced and becomes minus tolerance, the resulting overload on the bearings dictates that a printing operation cannot be started at that time, since the bearing gap is in an improper range at that time. Although the temperature of the surface of the plate cylinder may be stable, it is an improper condition while a temperature differential exists between an outer peripheral surface of the bearing and an inner peripheral surface of the bearing. A printing operation cannot be commenced until the temperature differential is reduced to a predetermined level.
In an intaglio printing press, large printing presses are required, this requiring that the bearings and the bearing housings be large in size. A longer time period (for example, more than eight hours) is needed to raise the temperature of the bearings to a stable temperature.
Such a problem exists not only in an intaglio printing press, but also in other types of printing presses that require heating a plate cylinder.